The effect of environmental pH on the proton motive force of Helicobacter pylori

BACKGROUND & AIMS: Responses of the proton motive force (the driving force for protons) in Helicobacter pylori to varying medium pH may explain gastric colonization. The aim of this study was to determine the effect of external pH (pHout) on the proton motive force, the sum of the pH gradient, and the potential difference across the bacterial membrane. METHODS: Intracellular pH (pHin) was measured by bis-carboxyethyl-carboxy fluorescein fluorescence and transmembrane potential difference (PD) by fluorescent quenching of 3,3'-dipropyl thiadicarbocyanine iodide at differing pHout and was correlated with survival. RESULTS: PD was -131 +/- 0.36 mV (n = 3), and pHin was about 8.4 at loading pHout 7.0. PD increased as pHout was increased from 4.0 to 8.0, giving a constant proton motive force of about -220 mV. Outside these limits, PD collapsed irreversibly to zero. Addition of 5 mmol/L urea to weak buffer at pH 3.0 or 3.5 prevented irreversible collapse of PD by elevation of pHout caused by NH3 production. Urea addition to weak buffer at pH 7.0 collapsed the PD as urease activity increased the pHout to about 8.4. Survival was also limited to this range of pHout. CONCLUSIONS: H. pylori survives over the range of pHout where it maintains a proton motive force. The effect of urease activity on pHout, while allowing gastric survival in acidic media, may limit survival in nonacidic media.     

Pattern recognition classification of the site of nephrotoxicity based on metabolic data derived from proton nuclear magnetic resonance spectra of urine

The computer-based pattern recognition procedures of nonlinear mapping and principal-component analysis have been applied to analyze 1H NMR-generated metabolic data on the biochemical effects of 15 acute nephrotoxin treatments affecting the renal cortex and/or renal medulla in rats. The 1H NMR signal intensities for 16 urinary metabolites representative of several major intermediary biochemical pathways were estimated using either a simple semiquantitative scoring system or complete peak intensity quantitation. NMR-derived data were treated as input coordinates in a multidimensional metabolic space and were analyzed by pattern recognition methods through which the dimensionality was reduced for display and categorization purposes. Different nephrotoxin treatments were initially classified using semiquantitative metabolite scores on the basis of their 1H NMR-detectable biochemical effects, and a good separation of renal cortical toxin treatments from renal medullary toxin treatments was achieved. The refinement of using exact peak heights rather than metabolic data scores utilized the available metabolic information more fully and provided a unique classification of each type of toxin according to its pattern of biochemical effects and site of toxic action. Principal-component analysis provided consistently better results than did nonlinear mapping in terms of discrimination between different sites of toxicity, and maps generated from correlation matrices gave improved discrimination, compared with those based directly on the original metabolic data. A comparison between the use of an added internal quantitation standard (3-trimethylsilyl-[2,2,3,3-2H4]-1-propionate) and independently determined glucose excretion rates for scaling to the NMR-detected urinary glucose levels demonstrated that the consistent classification of site-specific nephrotoxicity was independent of the quantitation standard used. This study has provided a rigorous assessment of data processing, relative quantitation, and pattern recognition methods, and the utility of applying these methods to the classification of NMR-derived toxicological data. The considerable potential of the NMR-pattern recognition approach in the assessment of nephrotoxicity has also been confirmed with the discovery of new combinations of molecular markers of renal cellular damage.     

Effects of distinctive features on recognition of incomplete pictures.

Conducted 2 experiments to determine the effects of distinctive features on recognition of incomplete pictures. Two sets of fragmented picture stimuli were designed: Set A preserved 75% and Set B preserved 25% of the distinctive features of the objects pictured. Within each set of stimuli, a complete (C), an intermediate (I), and a most incomplete (MI) representation of the objects was constructed. In Exp I, 60 Ss of 3 different age groups (3–4 and 5–6 yrs and undergraduates) were tested on the MI representations of either Set A or Set B. Results indicate significant differences in the age groups and in stimulus sets. In Exp II, 36 children (mean age 4 yrs 6 mo) were trained on either the C or the I Set A or the I Set B representations. After a day's delay, the Ss were tested on Set A or Set B MI representations of the objects and to novel representations. Results show significant differences among training conditions and in the test of the stimulus sets. The concepts of filtering and abstraction of distinctive features as discussed by F. J. Gibson (1969) are used in interpreting the results. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of sample freezing on proton magic-angle spinning NMR spectra of biological tissue

Magic-angle spinning (MAS) has recently been shown to enhance spectral resolution in NMR examinations of intact biological tissue ex vivo. This work demonstrates that freezing certain tissue samples before examination by 1H MAS NMR can have a marked effect on their spectra. Spectra of rat kidney after freezing in liquid nitrogen, compared with spectra before freezing, showed a significant increase in signal intensities from alanine (>100%), glutamine (>40%), and glycine (>100%), and a decrease in signals assigned to lipids and other macromolecules. Some resonances--such as from leucine, valine, isoleucine, and aspartate--only became visible after freezing the tissue. These observations suggest that low temperature storage of tissue necropsies or biopsies might affect the results of a MAS NMR analysis, possibly resulting in the misinterpretation of metabolite changes to pathogen or disease effects.